Characterizing Turbulence Modification via Red-Blood-Cell Analogs in Free Shear Layers using Particle Tracking Velocimetry

The turbulence modification of red blood cells is evaluated using a basic experimental approximation to blood, which specifically accounts for its particle-laden and dense concentration in vivo. The contribution of super absorbent polymer beads to a developing free shear layer is quantified using particle tracking velocimetry. Results showed that the presence of a particle-phase reduced mean velocities, kinetic energy, and the gradient of kinetic energy, implying that the free shear layer was diffused. Furthermore, similar fluid behaviour resulted between the suspension cases when Reynolds number was increased from 1,143 to 10,490. This suggests that red blood cells act to diffuse flow features that can subsequently lead to instabilities from which transitional and eventually turbulent behaviour can develop. These findings indicate that a two-phase model, specifically accounting for the dense particle-phase of blood, may be necessary for arterial blood flow where transition and turbulence can occur

Catalytic Performance of Micro-Mesoporous Zirconosilicates Prepared by Non-Hydrolytic Sol-Gel in Ethanol-To-Butadiene Transformation and Related Reactions

Synthesis of 1,3-butadiene (BD) from ethanol has experienced a true renaissance in recent years due to ecological and economic reasons. The open porosity and number of Lewis acid sites in metal silicates (M = Zr, Ta) have been reported in numerous studies as key factors enabling reaching high BD productivity. However, some microporous zeolites recently displayed very high BD productivity. To gain a deeper insight, we have applied non-hydrolytic sol-gel (NHSG) – a method well-known to produce highly porous and homogeneous metal silicates – in the preparation of zirconosilicates with varying micropore volume. The porosity (N2 adsorption-desorption experiments), structure (IR, XPS, NMR, and DRUV-Vis spectroscopy, XRD, MAS NMR), and acidity (IR spectroscopy combined with pyridine adsorption) of these materials have been described in detail and compared to a benchmark sample prepared by dry impregnation. Above mentioned characterization methods proved that NHSG preparation provided highly homogeneous Zr dispersion in silica leading to almost doubled Lewis acid site numbers and higher activity in ethanol-to-butadiene (ETB) transformation, Meerwein-Ponndorf-Verley (MPV) redox reaction, and aldol condensation, in comparison to the catalyst prepared by dry impregnation. The fraction of micropore volume in micro-mesoporous samples (ranging from 27 % to 69 %) did not play a significant role: The activity in all three catalytic reactions followed the acid site numbers. The selectivity and long-term stability in ETB process were similar for catalysts prepared by NHSG and dry impregnation

Effect of Enhanced Accessibility of Acid Sites in Micromesoporous Mordenite Zeolites on Hydroisomerization of <i>n</i>‑Hexane

This paper describes a study of the nature and the accessibility of the acid sites in micromesoporous mordenite zeolites obtained by desilication and dealumination and analysis of their activity and selectivity in the hydroisomerization of <i>n</i>-hexane. Alkaline–acid, acid–alkaline–acid, and fluorination–alkaline–acid postsynthesis treatments were employed for the preparation of micromesoporous mordenites. The FTIR spectra of adsorbed <i>d</i>₃-acetonitrille, ²⁷Al MAS NMR, HR-TEM, and N₂ adsorption were used for quantitative analysis of the Brønsted and Lewis sites, the coordination of Al atoms, and the textural properties. The alkaline treatment causes desilication, preferably occurring along the crystal defects and resulting in the formation of a secondary mesoporous structure characterized by 5–20 nm cavities and the formation of extraframework (Al_Ex) species and terminal Si–OH groups. The Al_Ex species formed by hydrolysis of perturbed or dislodged framework Al easily restrict part of the pseudomonodimensional channel structure of mordenite. The subsequent removal of Al_Ex by mild acid leaching or simultaneous removal of Si and Al atoms by desilication of fluorinated zeolite result in a micromesoporous structure with a large number of unrestricted channel openings and lead to a large increase in the accessibility of OH groups for <i>n</i>-hexane. Thus, the sequential leaching treatments enable the formation of active acid sites in an environment of nonrestricted microporous channels with simultaneous enhancement of accessibility of the active sites and molecular transport. It is shown that the micromesoporous structure with high concentration of Brønsted sites of enhanced accessibility directs the hydroisomerization reaction toward high yields of branched isomers and shortening of the main 12-ring channels and that the larger numbers of channel openings result in an increase in selectivity, limiting nonselective subsequent cracking reactions